Edge cracking occurs along a blank edge that is strained by shearing in a trim operation and is one of the failure modes for stamping processes. The edge cracking phenomenon is more commonly observed AHSS and Aluminum applications. In draw operations, edge stretch may be observed, for example, in body side outer assemblies, door inner panels and developed blank structural panels. Edge cracking due to stretch flanging commonly occurs in secondary forming (e.g. reform/flange die etc.) operations. A developed blank or hole/cut-off after a drawing operation may be processed in a trim die, blanking die or trim/pierce die.
Referring to FIG. 1, one example of a prior art trim die set 10′ is shown in FIG. 1 is diagrammatically illustrated that includes a pad 12′ that clamps a sheet metal blank 14′ against a first die 16′. A second reciprocating die 18′ includes a trim steel 20′ moved by the second reciprocating die 18′ in a press (not shown) to trim the sheet metal blank 14′ along a trimmed edge. Blanking and trimming processes are shearing processes. Shearing creates a work-hardened area at the trimmed edge and may create micro-cracks along the sheared edge. Work-hardening and micro-cracks reduce ductility and cause edge cracks in subsequent forming operations.
In an attempt to improve edge stretch characteristics, process parameters such as cutting tool clearance may be adjusted. Entirely different processes have been proposed to trim or blank work pieces such as shaving, bevel shearing or fine blanking. The other proposed processes have only achieved limited improvement in reducing edge cracks or add cost to the manufacturing process.
This disclosure is directed to solving the above problems and other problems as summarized below.